Q: I’m moving house. Can I remove the Mezuzahs from my old house?
A: As a general rule, Mezuzahs should not be removed from doorposts, leaving the room(s) or house without a Mezuzah. Exceptions to this rule are when one removes a Mezuzah with the intention of putting it back or replacing it with another one.
Therefore, in the case of one who is moving house; if the new tenants are Jewish the Mezuzahs should not be removed. In the case of one who worries that if he leaves his Mezuzahs they will be discarded or defaced, they may be removed.
In the case of a new occupant who has his own Mezuzahs and therefore does not want yours, it is preferable that he remove your Mezuzahs before installing his or that at least he should request from you to do so. One should not dismiss this matter as a light one because actually this law is a very serious one and in the case of doubts on how to proceed, one is best off asking a competent Rabbi for advice.
In the case of a new occupant who wants your Mezuzahs, one is obligated to leave them in place. If your Mezuzahs are expensive and of high quality, one can replace them with less expensive ones before leaving as long as they are kosher. In the case of Mezuzah cases, they can certainly be exchanged for inexpensive ones.
In the case of one who is moving and temporarily owns and lives in two homes, one is obligated to have Mezuzahs in both homes.
Q: I removed my Mezuzahs. How do I go about re-affixing them?
A: in the case of a Mezuzah that has been removed from the doorpost, in the case of renovations, for checking or whatever other reason, the Mezuzah is re-affixed and the blessing should be recited if the Mezuzah was off the doorpost for at least one night. If one is also putting up new Mezuzahs, it is preferable to recite the blessing over a new one, providing that it is mounted on a door that requires a blessing.
It is preferable that one return each Mezuzah to its original doorpost, or at least to the same type of entrance way (e.g. from one bedroom doorpost to another).
Practically speaking, it is advisable to label each Mezuzah that is removed with a number (using masking tape). Tape an identical number onto the doorway from which it was removed. In the case of Mezuzahs that are getting checked, make sure to as k the scribe to return each scroll to its original case. That way, when the time comes to reaffix the Mezuzahs, one simply needs to match the numbers on the Mezuzahs to the numbers on the doorposts.